> if the key is missing today you'll get nil as the value
You can add a third parameter to override the nil if detecting the missing key matters.
(You almost surely know this, but not all HN commenters will.)
You can add a third parameter to override the nil if detecting the missing key matters.
(You almost surely know this, but not all HN commenters will.)
user> (:bar {:foo 1})
nil
user> (:bar {:foo 1} :missing)
:missing
免责声明：我担任 Cimpress 的物流、优化和运营副总裁，但这里的所有观点都是我的，而不是 Cimpress 或 Vistaprint 的。